Titanium alloys, aluminum alloys, and steels have physical and chemical properties that are often desirable for a wide variety of static structural applications. However, these alloys often do not provide the wear and corrosion resistance that is required in many rotating or reciprocating machine applications such as in aircraft propeller blades, compressor turbine blades, bearings, pistons, and similar wear parts and dynamic machinery components. For example, titanium alloys have attractive properties such as high specific strength and stiffness, relatively low density, and excellent corrosion resistance, but titanium alloys typically have poor resistance to wear and oxidation at high temperatures. Aluminum castings are light in weight but provide little resistance to galling and other wear-related phenomena even at moderate temperatures. Steels have high strength and may be surface hardened by such techniques as nitriding and carbiding, but still the wear resistance of such surface-hardened steel alloys is inadequate for many applications.
Techniques such as plasma spraying, sputtering, and plating have been developed to add a wear resistance layer to the surface of metal substrates. However these techniques often result in distortion of substrate geometry, reduction of surface smoothness, and eventual delamination of the added layer from the substrate. Therefore better materials and techniques are needed for improving the corrosion and wear resistance of the surfaces of metals.